500 lb. Mk82 bombs and others of its era are constructed using vintage technology. Such bombs have been in the U.S. weapons inventory for a number of years.
500 lb. Mk82 bomb casings are made from a single-piece, cylindrical tube of low carbon steel that is shaped into the desired cigar-shape. Inserts, such as suspension lugs and access plates, are connected to the casing by filler metal welding techniques. An end member is attached to the open back end of the casing by filler metal welding techniques or by screwing a threaded version of the end member into a threaded open back end on the casing. The casing also may be formed with an integral end member, obviating the need to attach the end member by any of these methods.
500 lb. Mk82 bombs are ineffective against hardened targets such as aircraft shelters, runways, command bunkers, ships, dams, bridges, and armored vehicles. Mk82 bombs upon impacting such targets ricochet off or the casing prematurely breaks up. In either situation, the target is not destroyed. Hence, there was a need for bomb casings of advanced technology that would be part of a bomb effective against hardened targets.
New technology has been developed for constructing bombs with casings made from high strength alloy steel. Heretofore, preferably, these casings have been of single-piece construction. It was necessary to construct the casings in this manner so that they would have the requisite strength and fracture properties. Bombs that incorporated these single-piece casings have been found effective against hardened targets.
The constructive methods for making single-piece casings of high strength alloy steel include forging, casting, or extrusion. One problem with making single-piece casings by these methods is that the equipment for making such casings is in limited supply. Another problem in making single-piece casings is they are expensive.
This new bomb casing technology also has contemplated making multi-section casings. Multi-section casings are less expensive to make than single-piece casings.
A method of making multi-section includes using a two-piece casting or forging of high strength alloy steel. The two pieces are joined by filler metal welding techniques. This method is slow and the welds are susceptible to cracking during heat treatment because of the inability to match exactly the filler and base metals. Hence, casings made by this method, in many cases, do not have the desired strength and fracture properties of single-piece casings.
Multi-section casings also have been made from two-piece forgings in which the sections are joined using electron beam welding techniques. Although acceptable casings have been produced, the method is extremely slow. If the rate of production is increased beyond the normal extremely slow rate, the welds are of inferior quality and susceptible to cracking.
The present invention overcomes these problems and provides a process for making multi-section bomb casings of high strength alloy steel at a reasonable production rate that have the strength and fracture properties of single-piece casings.